For various reasons associated in particular with greater comfort of use (softness, emollience and the like), current cosmetic compositions are usually in the form of an emulsion of the oil-in-water (O/W) type consisting of an aqueous dispersing continuous phase and an oily dispersed discontinuous phase, or of an emulsion of the water-in-oil (W/O) type consisting of an oily dispersing continuous phase and an aqueous dispersed discontinuous phase. O/W emulsions are the ones most sought in the cosmetics field, since they comprise an aqueous phase as external phase, which gives them, when applied to the skin, a fresher, less greasy and lighter feel than W/O emulsions.
Standard O/W emulsions are generally stabilized with amphiphilic molecules of low molar mass (<5000 g/mol), such as emulsifying surfactants of the alkylglycerol or alkylpolyoxyethylene type. However, these surfactants have the drawback of inducing a waxy, heavy feel.
Moreover, it has been envisaged to replace surfactants with amphiphilic polymers, comprising in their chain a hydrophilic portion and a hydrophobic portion consisting of a fatty chain, such as copolymers of a C10-C30-alkyl acrylate and of acrylic or methacrylic acid, for instance the products sold under the name Pemulen by the company Noveon. However, these polymers thicken the compositions and thus have the drawback of not allowing fluid compositions to be obtained. Moreover, emulsions stabilized with polymers of this type comprise oil drops of relatively large size, which does not allow an acceptable stability to be obtained for low viscosity levels, the instability being reflected especially by rapid creaming, i.e. a rise of oil to the upper part of the emulsion, which is reflected by a phase separation with a white phase at the top of the bottle and an aqueous clear phase at the bottom of the bottle.
In addition, it is known practice from EP-A-1 069 142 to use amphiphilic polymers of α,β-ethylenically unsaturated monomers and of hydrophobic monomers, obtained by free-radical polymerization of a macromonomer containing a hydrophilic block of polyoxyalkylene type and a hydrophobic block containing from 1 to 30 carbon atoms, these polymers possibly being used as thickeners, emulsifiers, dispersants and suspension agents, especially in cosmetics. However, the polymers illustrated in the said document do not produce O/W emulsions with cosmetic properties that are very pleasant for the user while at the same time being very stable and easy to produce.
There is thus still a need to produce O/W emulsions based on amphiphilic polymers, which overcome the difficulties of the prior art, i.e. which are particularly advantageous in terms of cosmetic feel, while at the same time being easy to produce and having good stability.